This invention relates to a sensor effective to measure the operating parameters of an internal combustion engine. It particularly relates to such a sensor effective to generate output signals in response to both engine vibration and temperature.
It is known to provide an internal combustion engine vibration sensor of the type employing a piezoelectric disc in a housing having means effective to transfer vibrations of the engine into flexures of the piezoelectric disc. Such a vibration sensor is shown in the U.S. Pat. No. to Keem 4,254,354 issued Mar. 3, 1981; and many other examples are known. Engine vibration sensors using piezoelectric elements may be used for knock detection or the detection of other engine vibrations characteristic of specific engine operational events. In addition, engine temperature sensors of various kinds are known to be effective to generate a signal indicative of the temperature of some portion of the engine or of the engine cooling fluid, although the inventor is not aware of any such engine temperature sensor employing a vibrating piezoelectric element as the temperature sensitive element.
Engine vibration and temperature sensors are merely two of the many kinds of sensors employed in today's precisely controlled engines. In fact, the sensors of the engine control system can constitute a substantial portion of the cost of such engine controls; and a reduction in the number of such sensors may well help to reduce such costs. Although the day of the single sensor engine control system may not yet be at hand, attempts have been made in the prior art towards such a goal. One such attempt is the multifunction engine sensor of the U.S. Pat. No. to Andrews et al 4,299,117, issued Nov. 10, 1981. This is actually two separate sensors--a piezoelectric acoustic electric sensor and a thermistor temperature sensor--enclosed in a single package. The thermistor provides a signal of engine cooling temperature at one output terminal while the piezoelectric element provides an acoustically derived engine vibration signal on a different output terminal.